This invention relates to drive couplings and more particularly to linearly movable drive couplings disposed in a sealed final drive housing.
In track laying vehicles, it is sometimes necessary to permit towing of the vehicle. To facilitate towing, it is desirable to disengage the power transmission from the drive sprocket. Generally, a final drive planetary is disposed between the transmission output shaft and the drive sprocket and a drive coupling is connected therebetween. The drive coupling is manually movable between engaged and disengaged positions to permit the drive sprocket to be connected with the transmission output or freely rotatable, respectively.
It is also desirable to prevent dirt, water and other atmospheric contaminants from entering the drive sprocket. To this end, a lip seal is generally provided which is slidably disposed on the drive coupling Such an arrangement may be seen in U.S. Pat. No. 4,491,037, issued Jan. 1, 1985, to Bullock and assigned the assignee of the present invention.
While these sealing arrangements operate satisfactorily, the movement of the drive coupling within the housing can cause a change in the pressure condition within the housing. For example, the coupling is generally movable inward towards the transmission to connect the drive. This movement results in a decrease in volume of air within the housing and thereby an increase in the pressure of the air within the housing. It is possible for this air pressure to cause the drive coupling to return to the disengaged position when such movement is not desirable.